This invention relates to a novel multibeam electron gun and to a novel method for assembling that gun. The novel gun and novel method can provide better alignment of successive grid apertures as compared with a prior gun design.
My U.S. Pat. No. 4,298,818 issued Nov. 3, 1981 describes an electron gun for use in a multibeam cathode-ray tube. That gun includes at least two spaced successive electrodes held in position from a common support. Each electrode comprises a single metal plate having three beam-defining apertures therein, which apertures are so aligned as to permit the passage of three electron beams. The sizes and shapes of the electron beams are determined in part by the sizes, shapes and alignments of the apertures. Apertures that are misaligned by as little as 0.125 mm (0.5 mil) can cause distorted beam shapes and degrade the performance of the tube.
Where there are three or more beam-defining apertures in each of two spaced single-plate electrodes, it is the practice to align the apertures of the electrodes, either optically or mechanically, from two apertures of each of the electrodes. While the positions of the apertures in each electrode are precisely prescribed, nevertheless there are necessary manufacturing tolerances present in the fabrication of these electrodes. Manufacturing tolerances allow the sizes and positions of the apertures in each electrode to deviate slightly from the bogie or designed values. Typical manufacturing tolerances allow variations in aperture sizes up to about .+-.0.008 mm (0.3 mil) and in spacings up to about .+-.0.0125 mm (0.5 mil). As a result, the apertures of one electrode usually are misaligned with respect to the corresponding apertures in the other electrode even though great care is taken to achieve the designed structure.